Geography Total Notes - PDF

GEOGRAPHY Section A THE PHYSICAL WORLD The structure of the earth 1 page The earth is made up of three main layers ∙ The crust ∙ The mantle ∙ The core Crust- Mantle-mesospher Core-baryshpere...

GEOGRAPHY Section A THE PHYSICAL WORLD The structure of the earth 1 page The earth is made up of three main layers ∙ The crust ∙ The mantle ∙ The core Crust- Mantle-mesospher Core-baryshpere lithosphere e Thickness Its thickness It is 2900km thick Outer -2175km varies from place thick to place Temperature Cool Over 2000ْ ᵒc About 5500ºC Mineral Continents- Iron, magnesium Iron and nickel content granite (SIAL) and silica collectively called Oceans - basalt NiFe rocks (SIMA) Position Outer most layer Middle layer Inner most State Solid rocks Semi-liquid Inner core - (molten) solid this is due to pressure exerted on it by the other # layers 1  Outer core - liquid THE CRUST ∙ Makes up continents and oceans floors ∙ It consists of two parts that is granite (SIAL) and basalt rocks (SIMA) CONTINENTAL (Sial) OCEANIC (Sima) Thickness 35 to 70 km on average 6 to 10km on average Age of rocks Very old rocks of over 1500 Very young rocks of after death under 200 million years Weight of rocks Lighter with an average 2.6 Heavier- average of 3.0 Nature of rocks Light in colour Dark in colour Numerous types Few types Granite Basalt CONTINENTAL DRIFT THEORY It was proposed by Alfred Wegner in 1912. He believed that about 300 million years ago, all existing continents were one super continent called PANGEA. It later broke into 2 hemispheres, that is, the northern and the southern hemisphere. The northern hemisphere was called LAURASIA and the southern was called GONDWANALAND. EVIDENCE TO SUPPORT THE THEORY ∙ Different coastlines on the opposite sides of continents fit like a jig-saw puzzle when put together e.g. eastern coast of North America and western coast Europe ∙ Similar rock types and structure are found in Brazil and West Africa ∙ Rocks of the same age are found along the western coast of Africa and Eastern coast of Southern America 2  ∙ Remains of dead plants and animals of the same type and age are found along the eastern coast of America and west coast of Africa. PLATE TECTONIC THEORY It was formulated in the 1960s by a number of scientists who studied earthquakes and volcanic activities. The theory is based on the premise that the earth’s crust consist of a series of plates (continental and oceanic plates). The theory is about the movement of plates and it tried to explain the continental drift theory. It suggests that the continents and the ocean floors are constantly in motion such that they move towards each other (converge/collide) by forces of compression or away from each other (diverge) by forces of tension. These plates are moved by convection currents produced by the heat in the mantle The continental plates (SIMA) carry continents while oceanic plates (SIAL) carry oceans. According to the theory there are 10 plates. These are: The diversion and collision of plates results in the formulation of some features such as: ∙ Zones of subduction ∙ Trench ∙ Mid-oceanic ridges ∙ Fold mountains ∙ Volcanic mountains chains etc There are three types of margins found during plate movement ∙ Constructive ∙ Destructive 3  ∙ Conservative/transform/passive FOLDING It refers to the bending of rocks due to plate movement (compression). Plate movement will result in rock layers having an up folded part called an anticline and the down folded part called syncline. The sides of a fold are called limbs. TYPES OF FOLDS 1. Simple fold formed when there is compression (almost of equal strength) from both sides. 2. Asymmetrical fold it forms when there is more pressure exerted one limb. The pressure results in one limb becoming steeper than the other due to the continued compression. 3. Overfold more compression continues, resulting in one limb being pushed over the other 4. Overthrust/thrust fault there is more and more pressure resulting in the rock cracking or developing a crack and one of the limbs is pushed totally over the other one. FORMATION OF FOLD MOUNTAINS There are 2 ways in which Fold Mountains can be formed. 1. Continental and oceanic plate collision/convergence ∙ Oceanic and continental plates collide due to compressional force ∙ Oceanic plate sinks (because it is denser) and continental overrides ( this happens at the subduction zone) ∙ A trench/ geosyncline develops between the 2 plate 4  ∙ Sediments are eroded from the continental plate and fill in the trench layer after layer ∙ More sediments accumulate in the trench (as there is continued erosion) ∙ Sediments are compressed and become compacted together to form sedimentary rocks ∙ Continued compressional force the rocks to be uplifted, crumpled, squeezed and stand up to form Fold Mountains. 2. Continental and continental collision (e.g Eurasian plate and African plate converging to give Atlas Mountains) ∙ 2 continental plates collide due to compressional force ∙ Neither of the plates sink as they are of the same density ∙ Due to forces of collision, trench/geosyncline develops ∙ Sediments accumulates in the trench and due to the weight of the sediments the continental floor subsides downwards ∙ The width of the trench decreases as there is continuous compression causing the sediments to increase ∙ Sediments are compressed and become compacted together to form horizontal sedimentary rocks ∙ Continued compressional force the rocks to be uplifted, crumpled, squeezed and stand up to form Fold Mountains. Examples of Fold Mountains Old Young Cape ranges (South Africa) Atlas (N. Africa) Appalachians (N.America) Alps (Europe) Urals Rockies (America) Welsh (U.K) Himalayas (Asia) (collision of Indo-Australian and Eurasian plate) 5  CHARACTERISTICS OF FOLD MOUNTAINS ∙ They have steep slopes ∙ They are of great vertical heights ∙ They have several peaks ∙ They have valleys ∙ They have parallel ranges ∙ They have lakes ∙ They are ice capped ∙ They have saddles ∙ They are usually forested DIFFERENCE BETWEEN OLD AND YOUNG FOLD MOUNTAINS Old Young/old They are low They are very high They have a broad peak They have a sharp/narrow peak They have a gentle slope They have steep slopes Have shallow valleys Form deep narrow valleys They are sparsely forested They are densely forested Ice capped top POSITIVE IMPACT OF FOLD MOUNTAINS ON HUMAN ACTIVITIES FEATURE HUMAN ACTIVITIES Scenic beauty Tourism Presence of mineral (in case of Mining volcanic eruption) Dense forests Lumbering Rangelands Pastoral farming Presence of lakes Arable and pastoral farming Wind ward slope influencing relief Agriculture rainfall Presence of peaks Satellite installation for 6  communication purposes OTHER IMPACTS OF FOLD MOUNTAINS Positive ∙ They act as wind breakers ∙ They can used for defence Negative ∙ Influences cold temperatures because of their heights ∙ Their steep sides result in thin soils ∙ They are climatic barriers as they influence less rain in the lee-ward side ∙ They are barriers to construction of communication links e.g. roads DISTRIBUTION OF FOLD MOUNTAINS They are found where: ∙ Plates converge ∙ In destructive plate margins FAULTING Fracturing of earth crust due to compressional, tensional and lateral forces Types of faults 7 lines 1. Normal fault it occurs when tensional forces acts on a rock resulting in one part of the rock displaced up and the other one thrown down. It may result in the formation of a rift valley. An escarpment may be formed. An escarpment is a steep slope formed on the raised block of a normal fault. 2. Reverse fault it occurs when compressional forces acts on a rock causing one block to be pushed up over the other block. It may result in block mountains/horsts. 3. Tear fault it occurs when tensional force acts on the crust 7  resulting in horizontal displacement of the crust. 4. Thrust fault it occurs when intense compressional forces act on a rock resulting in the rock cracking. FORMATION OF RIFT VALLEYS There are two theories that attempted to explain the formation of rift valleys. One relies on the tensional forces and the other one on the compressional forces Compressional Tensional 4 lines The earth crust experiences 4 lines The earth crust experiences movement due to compressional movement due to tensional 4 lines Two parallel faults will 4 lines Two parallel faults will develop develop 4 lines The block on either side of 4 lines The block in between faults is pushed up/raises sinks/subsides 4 lines A low lying depression called 4 lines It forms a depression like a rift valley is formed. The raised feature called a rift valley. The blocks forms block mountains raised blocks forms block mountains CASE STUDY: THE GREAT RIFT VALLEY OF AFRICA/ EAST AFRICAN RIFT VALLEY It is the largest rift valleys found around the world. FEATURES OF THE GREAT RIFT VALLEY OF AFRICA ∙ It has parallel faults ∙ It has steep slopes ∙ It is 7200km long with 5600km in Africa ∙ It is between 30-100km wide 8  ∙ It has 2 main branches ∙ It has several lakes.g Lake Malawi, Tanganyika, Turkana, Nyasa, Albert, Rudolf ∙ It has volcanic mountains ∙ It has river e.g White and blue Nile ∙ It has deep valleys ∙ It has block mountains IMPACTS OF RIFT VALLEYS ON HUMAN ACTIVITIES FEATURES HUMAN ACTIVITIES Great scenic beauty major tourist attraction Contain lakes and rivers great sources of water for irrigation Often have rich volcanic soils good for arable farming Have dense forests good for lumbering Volcanic activities influence mining They influence relief rainfall good for farming NEGATIVE IMPACT FEATURES HUMAN ACTIVITIES Steep slopes Influences soil erosion Its relief Is a barrier to construction of infrastructure VULCANICITY It is a process through which magma, ashes and gases are forced out to the surface of the earth. The magma can appear as flowing lava, volcanic bombs, fragments of rocks ash and dust. Magma can reach the surface through a o Vent (hole) 9  o Fissure (crack) When magma emerges at the surface it loses its gases and it is called lava. HOW VOLCANOES ARE FORMED - There is plate movement, either divergence or convergence (this leads to zones of instability) - The crust develops faults or cracks - Pressure is released and magma from the mantle will rise through the fault - This results in eruptions accompanied by ashes,cinders,broken rocks ( eruptions can be very explosive if magma has too much gas) - On reaching the earth surface, the magma loses its gases and is called lava. - The lava accumulates and features such as pipe, dykes, conelets are formed. - A cone shaped mound will be formed and thus a volcano. EXAMPLES OF VOLCANOES IN AFRICA - Mount Kilimanjaro Tanzania - Mount Kenya Kenya - Mount Cameroon Cameroon - Mount Drakensburg - South Africa - Mount Nyiragongo Democratic Republic of Congo STAGES OF VOLCANOES A volcano goes through 3 stages in its lifecycle: 1. Active- when a volcano is active and erupts frequently. There are about 700 active volcanoes around the world e.g Mount Etna, Mount St Helen in the USA, mount Cameroon. 2. Dormant/ sleeping volcano-these are volcanoes that erupt less 10  frequently or after a long time. E.g Mount Rainier (USA) 3. Extinct/dead volcano- volcanoes which has not erupted in their known history or those that longer erupts e.g Mount Kilimanjaro (Tanzania), Snowdon (Wales) DISTRIBUTION OF VOLCANOES This refers to areas where volcanoes are mostly found. These include the following: - Along plate boundaries - At the pacific ring of fire - Areas of weakness in the crust e.g where faulting occurs - Along mid-oceanic ridges - In volcanic islands e.g Madagascar - Western coast of South America - At the Great Rift Valley of Africa - On the North East of Asia - In the Caribbean Islands INTRUSIVE AND EXTRUSIVE VOLCANIC FEATURES 12 LINES INTRUSIVE FEATURES These are volcanic features which are formed within the crust. They are formed when magma cools and solidifies in the crust before reaching the earth surface. Examples are: 1. Batholith They are formed when magma accumulates and cools before reaching the surface of the earth. It normally forms the base of a mountain. Due to erosion, the batholiths may be exposed to the surface e.g Nyika Batholoth in Malawi 2. Laccolith They form when magma solidifies along the crust forming a flat 11  based,round topped feature fed by a pipe e.g Elkoub Oup in Algeria 3. Lipolith Magma solidifies along the crust forming a saucer-like depression e.g Bushveld region in South Africa 4. Dyke Magma finds its way and cuts across the crust and forms a wall-like feature along line of weakness e.g Dolorite in Lesotho 5. Sill Magma penetrates horizontally along the crust and solidifies to form a sill. E.g Three Sisters in the Cape Province of South Africa EXTRUSIVE FEATURES These are volcanic features which are formed when the magma, ashes and gases reaches the earth surface and loses its gases to become lava. EXAMPLES OF EXTRUSIVE FEATURES Volcanic mountains Lava plateau Caldera Geysers Hot springs etc TYPES OF LAVA BASIC/FLUID ACID/VISCOUS o highly fluid o highly viscous o dark coloured o light coloured o low silica content o high silica content 12  o erupts frequently and less o erupts less frequently and explosive violently o form gentle slopes o form steep slopes o takes a longer time to cool and o cools and solidifies fast solidify therefore flows longer therefore flows very short distances distances 4 LINES 4 LINES FEATURES OF VOLCANOES o Pipe- the channel through which lava rises o Crater- a shallow depression found at the top of the volcano o Vent- the opening/hole on the ground through which magma is release o Conelets the small parasitic cones that build when magma escapes on the sides of the volcano o Geysers when super heated water underground shoots/erupts explosively often forming a natural fountain e.g at the Yellowstone National Park (USA) o Caldera this is an enlarged crater. Can be formed in two ways, through - a violent eruption ( when magma erupts violently and the crater is blown away resulting in a very wide depression) - Subsidence- when the mountain becomes too tall and collapses forming a wide depression at the top. o Caldera/crater lake- forms when the crater or caldera is filled with water and becomes a lake e.g Lake Basumtwi in Ghana (caldera), Ngorongoro in Tanzania (crater) o Plug forms when magma hardens within a vent on an active volcano. o Dome forms when viscous lava erupts slows and solidifies to form a roughly circular mound shape protrusion. TYPES OF VOLCANIC CONES 1. Lava cone- it is made up of lava. Its slope depends on whether the 13  lava is fluid or viscous. Fluid lava forms gentle sided slopes and vicious forms steep sided slopes. E.g Nyamlagira near Lake Kivu in DRC (fluid lava) and Hoggar mountains in Algeria (viscous) 2. Composite cone- it is formed of alternating layers of lava and ash. The volcano begins each eruption with great violence forming a layer of ash. As the eruption proceeds, the violence stops and lava pours forming a layer on the top of the ash. It has a large crater which smaller develops. Conelets may also form on the sides of the main cone E.g Mt Kilimanjaro 7 LINES 3. Ash and cinder is formed when lava is blown to great heights when it is violently ejected and it breaks into small fragments which fall back to earth and build up to form a steep sided cone. 5 LINES IMPACTS OF VOLCANOES ON HUMAN BEINGS Positive/advantages FEATURE HUMAN ACTIVITY Fertile volcanic soils Arable production Great scenic beauty encourages tourism e.g Mount Kilimanjaro Presence of minerals encourages mining Give rise to important caldera and Domestic and industrial water crater lakes supply Give rise to important caldera and Fishing crater lakes Give rise to important caldera and Irrigation crater lakes 14  Hot springs for medical purposes Geysers For geo-thermal power Thick forests for lumbering Negative/disadvantages o Danger/destruction of human life and property during eruptions o Very cold because of great heights o Some have steep slope hence have thin soils for agriculture to be carried out o Destroys the vegetation o Causes environmental pollution in the form of dust and gases (carbon monoxide) o People can become ill because of breathing in ash and poisonous gases. o Presence of lahar ( mudflow which is a mixture of ash and water) which blocks roads and railway lines also making communication difficult NEGATIVE IMPACTS OF VOLCANOES ON THE ENVIRONMENT ∙ Causes pollution with volcanic gases and dust ∙ Triggers earthquakes ∙ Destroys the vegetation ∙ Causes Tsunamis/tidal waves which leads to floods which drowns and kills people destroy people’s property ∙ Causes acidic and thin soil FISSURE ERUPTION ∙ It is a huge upland which is flat at the top with steep sides ∙ It is usually very quiet ∙ The lava comes out through fissures or small cracks in the earth’s crust 15  ∙ The lava spreads out over the surrounding area layer upon layer to form a lava platea WHY SOME VOLCANOES ERUPT VIOLENTLY. Magma contains gases, which are under great pressure. In some, there is a sudden decrease in pressure in the rising magma and this causes the gases in it to expand very rapidly. The sudden expansion can cause violent explosions. WHY SOME AREAS IN AFRICA EXPERIENCE VOLCANIC ACTIVITY ∙ Some areas are near areas of instability/plate boundaries ∙ Some areas experience earth movements due to tension and compression forces ∙ Some areas have cracks or are experiencing faulting ∙ Some areas experience tremors /earthquakes EVIDENCE OF VOLCANIC ACTIVITY IN AFRICA ∙ Presence of volcanic mountains ∙ Low lakes/calderas ∙ Associated volcanic features-intrusive features (batholiths, laccoliths, sills, dykes) and extrusive features (hot springs, lava plateaus, geysers, craters) WHY SOME VOLCANIC SLOPES ARE SPARCELY POPULATED WHILE SOME ARE DENSELY POPULATED SPARCELY DENSELY - Still active - Are dormant/extinct - Have steep slopes - Have gentle slopes - Are too cold - Water supply from lakes - Have thin/infertile soils - Have fertile soils 16 - Rarefied air - Have clean air - Little rainfall - Have adequate rain fall - Prone to - Presence of pastures diseases/pests/epidemics - Acid rain - Ancestral connections - Employment opportunities in hotels for tourism - Availability of forests for lumbering 17 EARTHQUAKES Earthquake: The vibration/shaking or sudden movement of the earth crust. Seismology: the study of earthquakes Seismologist: a scientist who studies earthquakes Plate collision also results in the faulting of the crystal rocks thereby creating fractures or cracks through which magma can escape. When vulcanicity occurs, the earth crust is bound to shake, thus, earthquakes and volcanic actions and often associated. CAUSES OF EARTHQUAKES 1. Collision of tectonic plates along a line of fault 2. volcanic eruptions REGIONS OF EARTHQUAKES/DISTRIBUTION - Along plate boundaries - At the pacific ring of fire - Areas of weakness in the crust e.g where faulting occurs - Along mid-oceanic ridges - In volcanic islands e.g Madagascar - Western coast of South America - At the Great Rift Valley of Africa - On the North East of Asia NATURE OF EARTH QUAKES 12 lines The point at which an earthquake originates is called the focus. This takes place several kilometers below the earth’ surface. The energy in an earthquake travels as SHOCK WAVES from the focus. The type of shockwaves known as BODYWAVE travels through the crust to hit the surface of the earth. The point at which the surface is first hit is called EPICENTRE. 18 From the epicenter, shockwaves travel as SURFACE WAVES and spread to affect a wider area of the earth’s surface. There are two types of body waves which are: Primary wave - causes crustal waves to move or shake back and forth Secondary waves causes crustal rocks to move from side to side There are two types of surface waves namely: Love wave causes rocks to dance from side to side at right angle to the direction of wave movement Rayleigh waves causes rocks to vibrate in a vertical circular movement HOW EARTHQUAKES OCCUR - There plate movement/collision of plates - Faulting/folding occurs - Pressure/energy is released at the focus - Shockwaves radiate outwards/towards the epicenter - Vibrations are felt - The minor vibrations cause tremors and major vibrations causes earthquakes. EFFECTS OF EARTHQUAKES o They can destroy buildings, communication systems and other infrastructure e.g roads, telephone and electric poles o They can cause displacement of oceanic floors which result in flooding of coastal settlements o They may destroy natural vegetation and animal habitat o Can cause loss of life/injuries o Can cause tidal waves/tsunamis o Can cause mud flows o Destroy the earth’s scenery by opening up deep cracks. 19  o May lead to displacement of people/relocation o May cause destruction of farmland o May cause outbreak of fires HOW THE EFFECTS OF EARTHQUAKES CAN BE REDUCED o Predicting future earthquakes/early warning e.g planning earthquake regularity o Formation of disaster plans e.g training emergency services such as fire, police and ambulance crews o Construction of earthquake resistance building e.g use of steel frames which can sway during earthquakes o Evacuation/ use of rescue teams o Education about earthquakes o Construction of roads which provide quick access for emergency services o Enforcing strict building regulations WHY IMPACTS OF EARTHQUAKES VARY FROM PLACE TO PLACE ∙ Time of the day- during there could be fewer impacts since people are awake and can easily and quickly respond unlike at night. ∙ Distance from the epicenter- places nearer to the epicenter will experience more damage than those far. ∙ Structure of the rocks places with strong rock base may experience less damage as compared to those with weak rock bases. ∙ Depth of the focus- the deeper the focus the lesser the impact of the earthquakes and vice versa. This is because as shock waves travel longer distances to reach the earth surface they lose their strength. ∙ Strength of the earthquake stronger earth has larger impacts and vice versa. ∙ Population size places with less people have less impacts and vice versa. ∙ Distance from the sea places closer to the sea maybe affected by flooding and tsunamis as compared to those which are far. 20 DETECTING EARTHQUAKES The intensity of earthquakes refers to the effort produced or the strength of an earthquake. It is detected by an instrument called SEISMOGRAPH. The magnitude (size) of an earthquake is the total amount of energy produced. It is measured or recorded on a RICHTER SCALE, which ranges from 0 to 9. 12lines The greater the reading on the ritcher scale, the greater the extent of damage caused on the earth’s surface. WHY INTERIORS OF MOST CONTINETS DO NOT EXPERIENCE EARTHQUAKES ∙ It is far away from plate boundaries ∙ They are no plate boundaries ∙ It has stable plates/rigid plates WEATHER AND CLIMATE Weather the average condition of the atmosphere observed over a short period of time Climate - the average condition of the atmosphere observed over a long period of time Elements of weather need to be measured in order to obtain a picture of the weather. A weather station is a place where the weather elements are measured and recorded. Each weather station has a Stevenson’s screen. The Stevenson’s screen contains four thermometers: namely: - The maximum thermometer - Minimum thermometer - The wet bulb thermometer - The dry bulb thermometer 21